Boron nitride (BN) in all of its forms, including without limitation hexagonal BN (h-BN), BN nanosheets (BNNSs) and BN nanotubes (BNNTs), can be surface-functionalized with oxygen-containing functional groups, such as hydroxyls (—OH) or ethers (—OR), as well as with other functional groups, such as amino (—NH3), amine (—NHR), acyl (—COR), alkyl (—R) or halides (—X) moieties. For a comprehensive review of representative methods used to functionalize BN and potential applications of functionalized BN, see, e.g., Weng et al., Chem. Soc. Rev., 45, 3989-4012 (2016).
A number of specific applications have been reported for oxygen-functionalized BN (O—BN). As non-limiting examples, O—BN may be used as a catalyst for the oxidative dehydrogenation of propane to propene (Grant et al., Science, 1 Dec. 2016, DOI: 10.1126/science.aaf7885), as a non-toxic carrier for the delivery of anticancer drugs (Weng et al., ACS Nano, 8, 6123-6130 (2014)), as a thermal conducting filler in N-isopropyl-acrylamide hydrogels (Xiao et al., Advanced Materials, 27, 7196-7203 (2015)), as a hydrogen storage agent (Lei et al., Nano Energy, 6, 219-224 (2014), and as a water cleaning agent (Lei et al., Nature Communications, 4, 1777, DOI: 10.1038/ncomms2818 (2013)).
A number of methods are known in the art for synthesizing O—BNs. For example, Weng et al. (ACS Nano, 8, 6123-6130 (2014)) disclose synthesizing hydroxylated boron nitride ((BN(OH)x (x=0.6-0.9)) by dry mixing carbon nitride (g-C3N4) and boric acid. Notably, this method is a “pre” BN synthesis that does not use BN as a starting material.
As a second example, Liao et al. (Scientific Reports, 5, 14510, DOI:10.1038/srep14510 (2015)) disclose the oxidative etching of h-BN by dry mixing h-BN with silver acetate to produce Ag—BN, which is then etched with nitric acid. Notably, this method requires difficult separations and very high temperature conditions.
As a third example, Xiao et al. (Advanced Materials, 27, 7196-7203 (2015)) disclose a method of exfoliating and hydroxylating h-BN using a high temperature steam treatment.
Other methods known in the art for synthesizing O—BN include ball-milling BN with sodium hydroxide, and exposing BN to nitric acid.
Each of the known methods of synthesizing O—BN has one or more significant disadvantages, such as requiring numerous and/or complicated separation steps (e.g., vacuum filtration, washing), requiring difficult to manage reaction conditions, such as very high temperatures, requiring costly specialty equipment (e.g., ball-milling equipment, reflux condensers, filtration equipment), and/or exhibiting unacceptably low O—BN yields. Furthermore, the known methods do not exhibit the high yield recovery and scalability that are needed to support large-scale commercial production of O—BN.
Accordingly, there is a need for new and improved methods of producing O—BN that are less costly, exhibit higher yield O—BN recovery, and are more scalable than previously known methods.